1. Field of the Invention
The present invention relates to a hand-held power tool and, in particular hammer drill or chisel hammer, including a sub-assembly that vibrates along a vibration axis, a handle sub-assembly, and an antivibration element for vibrationally decoupling the handle sub-assembly from the first-mentioned sub-assembly.
2. Description of the Prior Art
Usually, in vibrating hand-held power tool, the handle is decoupled from vibration-transmitting parts to a most possible extent, with the handle being connected with a vibrating part or sub-assembly by an antivibration element. The antivibration element can have both spring and damping characteristics.
At infinitesimal stresses, each spring rate characteristic is linear, which is typical for low-loaded helical springs. At large stresses, dependent on material properties, the spring rate characteristic is increasingly non-linear, in particular, when elastomers are used. In addition, a spring with a non-linear spring rate characteristic can be realized by using a suitable spring geometry, e.g., a leaf spring, or by further constructive features such as, e.g., a one-side positive contact.
International application WO 94 16864 discloses an axially percussive hand-held power tool in which there is provided an antivibration element for decoupling a handle from an axially vibrating sub-assembly of the power tool and having a nonlinear spring rate characteristic that passes, on opposite sides of a lineal flat middle load region, smoothly into a progressive course. To this end, the antivibration element is formed as an elastomeric hollow cylinder or, alternatively, as a leaf spring hollow cylinder. The drawback of a hollow cylinder for use in damping of vibration of a hand-held power tool consists in its pronounced dependence on the temperature and humidity and in changes associated with aging. The metallic leaf spring hollow cylinder is an expensively produced complex part.
German Publication DE 10 2004 031866 discloses an antivibration element for vibration-damping of a handle of a vibrating hand-held power tool and which has an axial non-linear spring rate characteristic or curve. The known antivibration element consists of a spring wire coil spring with the opposite ends of the coil spring being wound on a threaded plug. The coil spring windings partially abut a side of the outer thread of the threaded plug the between-flight width of which is greater than the spring wire diameter. The obtained spring rate characteristic passes smoothly after a linear flat loading region in a progressively increasing stretch and then smoothly in a steep linear stretch. The core of the thread plug is, spring-side, axially convexly-diminishing, proceeding from the inner diameter of the coil spring.
The object of the invention is to provide a hand-held power tool with an antivibration element having an axial non-linear spring rate characteristic that has a steep stretch on both sides of a linear middle loading region.
Another object of the present invention is to provide a hand-held power tool with an antivibration element having an axial non-linear spring rate characteristic at a transverse loading.